1. Field of the Invention
The present invention relates to a novel class of antioxidants which are useful in functional fluids, particularly those which have shielded polysilicate compounds, silicate esters, or silicone oils as base fluids. More specifically, the present invention relates to the use of selected 4-hydroxyphenyl anilino alkoxysilanes as these antioxidants.
2. Description of the Prior Art
Antioxidants are widely used in many functional fluids, including those that have hydrocarbon fluids, silicate esters, and silicones as base fluids. They are used to prevent oxidation from degrading the fluid and, thereby, decreasing its performance.
It is generally believed that oxygen acts upon organic compounds, including functional fluids, by a free radical mechanism. These radicals may be initiated by thermal or mechanical cleavage of molecules in the functional fluid. Then, these radicals combine readily with oxygen to give peroxy radicals which then react in a number of ways depending upon the environment and the type of compound. The ultimate products may be ketones, alcohols, and carboxylic acids that may condense to polymer chains such as lacquers, gums, sludges, and the like. These latter materials may be corrosive or remain in the fluid, thereby increasing the viscosity of the fluid above operational levels. Conversely, cleavage products may form which reduce viscosity and increase volatility to unacceptable levels.
Antioxidants are used to prevent this oxidation process by reacting with the radicals before they form the polymer chains. Therefore, the propagation of polymer chains is inhibited and the properties of the functional fluid will change by a lesser amount, if at all, over a period of time.
Functional fluids having either shielded polysilicates, silicate esters, or silicone oils or mixtures thereof as base fluids have special problems in protecting them against oxidation because they tend either to form gels upon oxidation or to have a limited solubility, stability, or efficiency for most common additives in general and most common antioxidants in particular. Accordingly, there is need to find new antioxidants which may be easily used with many types of functional fluids, including shielded polysilicate compounds, silicate esters, and silicone oils.